1. Field of the Invention
The invention relates to impact-modified polycarbonate compositions which are distinguished by high heat resistance and good melt flow behaviour. In addition, the mouldings produced from the compositions according to the invention in an injection-moulding process can be metallised, the resulting metallised mouldings having a particularly high and, in particular, homogeneous gloss. The invention thus also provides the metallised mouldings produced from the compositions according to the invention.
2. Description of Related Art
In particular, the invention relates to housings mirror-coated by metallising and thus functioning as reflectors for car headlights and car rear lights, which are made from the polycarbonate compositions according to the invention, have adequate heat resistance and mechanical load-bearing capacity for the application and can be welded to a lamp cover consisting of a transparent polycarbonate or polymethyl methacrylate composition.
The use of polycarbonate compositions for the production of car lights is known in principle.
JP-A 2005119239 discloses a method for the laser welding of car light parts made of thermoplastic resins, wherein the first component is transparent and the second component is opaque. As examples, polycarbonate is disclosed as the transparent component and ABS as the opaque component.
DE-A 440-4604 discloses reflectors, particularly for car headlights, consisting of a rigid shell made of a thermoset material coated with a metallised film of a thermoplastic, wherein the thermoplastic is, for example, a polycarbonate or an ABS.
JP-A 3880142 discloses polycarbonate compositions with pearly gloss and high reflectivity, comprising 35 to 65 wt. % aromatic polycarbonate having a viscosity average molecular weight of 16,000 to 26,000, and methyl methacrylate polymer and acrylic elastomer in a weight ratio of 95:5 to 60:40, and the use of such compositions for the production of lamp reflectors.
JP-A 2002124109 discloses housing materials for car lights which are vapour-coated with a reflector layer made of aluminium, comprising 10 to 90 wt. % polycarbonate and 10 to 90 wt % rubber-modified styrene resin, wherein the materials have a rubber content of 1 to 7 wt. %. No mention is made in this application of any advantages that may arise from a special size of the rubber particles in the rubber-modified styrene resin. The rubber-modified styrene resin used in the disclosed examples is an ABS consisting of 50 parts by weight of butadiene, 15 parts by weight of acrylonitrile and 35 parts by weight of styrene with a particle size of the rubber backbone of 350 nm.
JP-A 10287802 discloses polycarbonate compositions and their use as a housing material for car lights with good heat resistance, solvent resistance, weathering resistance, weldability and metallisability, comprising 30 to 65 parts by weight of aromatic polycarbonate, 5 to 40 parts by weight of graft polymers produced by grafting aromatic vinyl monomers and vinyl cyanides on to acrylate-comprising rubbers, and 20 to 50 parts by weight of copolymers of vinyl monomers and vinyl cyanides.
It is also described in the literature that technical advantages may be obtained from special particle size distributions of the rubber particles in rubber-modified polycarbonate compositions.
EP-A 704 488 discloses polycarbonate compositions with improved low-temperature resistance comprising 15 to 80 parts by weight of thermoplastic polycarbonate, 4 to 40 parts by weight of graft polymer based on rubber particles as the backbone and 16 to 45 parts by weight of thermoplastic vinyl aromatic (co)polymer, wherein the backbone has an average particle size (d50) of 200 to 350 nm and graft polymer and vinyl aromatic (co)polymer are used in a weight ratio of between 2:1 and 1:4.
EP-A 606 558 discloses polycarbonate compositions with improved melt flow behaviour and increased modulus of elasticity in bending, comprising 55 to 90 wt. % of aromatic polycarbonate, 10 to 30 wt. % of a graft polymer based on a particulate diene rubber backbone and 0 to 15 wt. % of a vinyl aromatic copolymer, wherein the diene rubber backbone has a narrow, monodisperse particle size distribution, characterised in that more than 50 wt. % of the particles have a diameter of between 200 and 300 nm and more than 70 wt. % of the particles have a diameter of between 200 and 400 nm.